Chapter 4: DISCUSSION
4.2.2. Discussion on the centile chart of resistive index (RI) for gestational age from 22 to 37 weeks
In our study, in normal pregnant women at 22-37 week’s gestation, the RI was closely correlated with gestational age. The correlation coefficient between the RI and gestational age compared with other authors in the world showed that most authors selected a first-order function such as Bahlmann, Tongparset.
Comparison of the correlation function between the RI and the gestational age of the authors in the world showed that the authors constructed a histogram of the RI for gestational age with the 1st and 2nd order functions. In this study, we selected the third-order function because we found that the third-order function had a higher correlation coefficient and indicated the variable rule of RI decreased with increasing gestational age more accurately. Differences in correlation functions may be due to gestational age at study start, study method, data analysis methods of different authors.
Our findings suggested that the DVRI decreased with gestational age.
The results of our study were also consistent with some other authors in the world. The value of the DVRI decreased steadily as gestational age increased, reflecting the RI of decreased placental circulation, suggesting that the circulation in the placental papilla facilitated easy maternal and fetal metabolism. It facilitated the development of the fetus without the risk of fetal growth retardation in the uterus. Therefore, when the DVRI was normal, the risk to the fetus was very low. Studies showed that the DV Doppler RI were different and had characteristics among different racial groups. Therefore, it is necessary to develop physiological constants of DVPI for each population race .
4.2.3. Discussion on the centile chart of S/a ratio of the ductus venosus for gestational age from 22 to 37 weeks
Since 1994, Rizzo et al and others found a strong correlation between gestational age and the S / a ratio, whereas gestational age increased with decreasing the S / a ratio. Our study in pregnant women with gestational age from 22 to 37 weeks, the S / a ratio was closely correlated with gestational age.
The S / a ratio of the ductus venosus was strongly correlated with gestational age and tended to decrease with gestational age, suggesting that the circulation in the placental papilla facilitated the easy metabolism between the mother and the fetus. , facilitating the development of fetuses without the risk of fetal development retardation in the uterus. The S / a ratio of the ductus venosus decreased with increasing gestational age in our study, which was consistent with findings of many authors in the world.
All studies found that the S / a ratio was closely correlated with gestational age and decreased as gestational age increased in line with the physiology of placental circulation. Studying the S / a ratio of the ductus venosus for gestational age to establish the centile chart was very significant in practice, as demonstrated by studies worldwide that was the basis for normal pregnancy monitoring. This helped to detect abnormal pregnancies.
The S / a ratio of the ductus venosus varies between countries. It demonstrates that the centile chart of the S / a ratio of the ductus venosus was specific to each country. Thus, it is necessary to develop the physiological constants for the S / a ratio of DV Doppler for each population race.
4.2.4. Discussion on the centile chart of mean folow velocity and velocity of waves of S, D, a of the ductus venosus for gestational age from 22 to 37 weeks
The exploration of Doppler at the entry site of the ductus venosus will show an increased blood flow rate due to the sphincter of the ductus venosus . Tightening at the entry site from the umbilical vein into the ductus venosus results in increased blood flow. Studies have shown that the blood flow rate through the ductus venosus increased with gestational age. Indicators of blood flow velocity in the ductus venosus were strongly correlated with gestational age in terms of second order functions with the highest correlation coefficient. References to international studies showed that the authors selected different correlation functions, but all agreed that the wave velocity was strongly correlated with gestational age and increased with increasing gestational age. We selected the second - order function because it had the highest correlation coefficient reflecting the development rule of the velocity index increasing with increased gestational age. This is also perfectly suited to the physiology of fetal circulation and placental one
Nakagawa et al conducted a cross-sectional study in 146 pregnant women with gestational age from 17 to 38 weeks, measuring the flow velocity of the S,D,a waves of the ductus venosus to establish a normal value for velocity and showed that the wave velocity increased when gestational age increased, demonstrating the growth of fetal cardiac function due to decreased RI of umbilical artery and placental artery increased blood flow to the fetus.
Marcolin et al studied the DV Doppler velocity index in 60 healthy pregnant women who did not have gestational pathologies in the second half of gestation, indicating: the velocity of waves of S, D, and a increased with gestational age from 20 to 40 weeks. Authors have established normal values for fetal flow velocities from 20 to 40 weeks and concluded that the flow velocity measurement through the ductus venosus was an important tool for assessing healthy fetuses and from this helped detect changes in fetal circulation.
All studies said that the blood flow velocity values of the ductus venosus were positively correlated to gestational age and having established normal values for each population race. It is important in clinical practice to help the follow-up of routine pregnancy and thus to help detect fetal abnormalities.
4.3. DISCUSSION ON APPLICATION OF THE CENTILE CHART OF DV DOPPLER INDICES IN FETAL GROWTH RESTRICTION 4.3.2. Evaluate the application of the centile chart of DV Doppler indices in this study for fetal growth retardation in the uterus:
The fetal growth restriction in the uterus is one of the major challenges in pregnancy care and management. When ultrasound, we found that estimated fetal weight was below the 10th centile line, we would use Doppler ultrasound and based on it to divide fetal growth retardation stages in the uterus:
Compared with the centile chart of DVPI in normal pregnancy, we found that the DVPI in fetal growth retardation was higher than that in normal pregnancy.
Our findings were similar to findings by authors in the world and showing that the PI, the RI, the S/a ratio of the ductus venosus were higher in fetal growth retardation in the uterus than those in normal pregnancy .
Wegrzyn et al conducted a study to compare the DV Doppler indices in fetal growth retardation and normal pregnancy. 208 pregnant women included in the study, in which 89 pregnant women with the 22-42 weeks of delayed growth in the uterus and 119 with normal pregnancy in the control group. Using Doppler ultrasound to measure PI, RI, S / a ratio. The authors found that for the normal group, these indices decreased with gestational age and for fetal growth retardation group in the uterus, these indices were significantly higher than those in normal pregnancies
Cruz-Martinez et al. (2011) conducted a study to evaluate a change of DV Doppler PI in 115 pregnant women with delayed growth fetuses in the uterus at a gestational age of less than 34 weeks. The authors found that the DVPI in fetal growth retardation in the uterus lying the 95th centile line before birth of 26 days, 12 days and 5 days. The authors suggested that the DVPI in fetal growth retardation could increase earlier, so the exploration of DV Doppler PI played an important role in monitoring and prognosis of fetal growth retardation in the uterus
Figueras et al. (2009) evaluated a change in Doppler PI in 46 pregnant women with delayed growth fetuses in the uterus at a gestational age of less than 34 weeks, the authors found that in the fetal growth retardation in the uterus, the PI of umbilical artery, the ductus venosus was greater than the 95th centile line. It is necessary to early detect changes of Doppler indices of the fetus. When there is abnormal flow of wave reversal or diastolic dysfunction, it is in late stage.
Studies have shown that most of the fetal growths retardation in the uterus exhibited the changes in the fetal circulation, umbilical artery abnormalities that appeared first then abnormalities of the cerebral arterial Doppler and eventually abnormalities of DV Doppler . At this time point, the exploration the DV had the value to help make a predictive diagnosis close to the fetal condition that helped the physician make the decision to stop pregnancy in a timely manner to avoid prematurely unnecessary interventions, especially in the cases of fetal development retardation that was still preterm.